1. Field of the Invention
The invention relates to a developing apparatus for developing an electrostatic image formed on an image bearing member by an electrophotographic process, an electrostatic recording process or the like, and is for use, for example, in a copying machine, a facsimile apparatus, a printer or the like.
2. Description of the Related Art
Generally, in multi-color image forming, use is made of a technique of developing an electrostatic latent image formed in accordance with external information with developers of plural colors, successively forming developer images (toner images) of plural colors on a photosensitive member which is an image bearing member, and successively or collectively superimposing these toner images of the plural colors on a transfer medium such as paper.
In such a multi-color image forming apparatus, there is a rotational type developing apparatus or a rotary developing apparatus comprising developing apparatuses for developers of plural colors, e.g. black, yellow, magenta and cyan, mounted, for example, on a rotary member (rotational type developing member) along the rotational circumference thereof, and there has heretofore been proposed and put into practical use a so-called rotational developing process of rotating the rotational type developing member to thereby move a necessary developing apparatus to a developing position opposed to a photosensitive member which is an image bearing member and perform a developing operation.
On the other hand, in conventional image forming apparatuses of an electrophotographic-type, and above all, a multi-color image forming apparatus for effecting color image forming, there is widely utilized a two-component developing process using a mixture of a nonmagnetic toner and a magnetic carrier as a developer. The two-component developing process, as compared with presently proposed other developing processes, has merits such as the stability of the quality of image and the durability of the apparatus, while on the other hand, the deterioration of the developer due to long-period endurance, particularly the deterioration of the carrier has been unavoidable and therefore, the work of interchanging the developer has become necessary with the long-period use of the multi-color image forming apparatus, and this has brought about increases in service cost and running cost.
There have heretofore been proposed several methods of solving such a problem in a case where this two-component developer is applied to the rotary developing apparatus. For example, there is a method of loading a rotational type developing member with an interchangeable developer supplying cartridge as an accessory of the developing apparatus, and effecting the supply of a developer containing a toner and a carrier and the collection of the developer (see, for example, Japanese Patent Application Laid-Open No. H6-308829).
In this developing apparatus, however, there is adopted a structure for collecting the developer overflowing the developing apparatus into the developer supplying cartridge by the use of a plurality of screws and therefore, the apparatus becomes large-scale and a control mechanism also becomes complicated. Also, when the developing apparatus of such a construction and the developer supplying cartridge are carried on the rotational type developing member, the diameter of the rotational type developing member becomes large and the multi-color image forming apparatus becomes bulky. Further, a carrying route for the developer is complicated and when the developing member is rotated, there is the possibility of the developer leaking.
So, particularly in the rotational developing process, there is put into practical use a developer discharging process of supplying a two-component developer to the developing apparatus and discharging the two-component developer from the developing apparatus by the utilization of a change in a gravity acting direction resulting from the rotational motion of the rotational type developing member.
For example, Japanese Patent Application Laid-Open No. H9-218575, as shown in FIG. 10 of the accompanying drawings, discloses a rotational type developing apparatus 101 having four developing apparatuses 200 equally provided on a rotational type developing member 101′ along the circumferential direction thereof. A developer cartridge 6 containing therein a developer to be supplied is provided in each of the four developing apparatuses 200. Design is made such that at a developing position P1 opposed to a drum-shaped photosensitive member (photosensitive drum) 113 as an image bearing member, the developer containing a toner corresponding to an amount consumed by a developing operation is supplied to the developing apparatus 200, and any excess developer in the developing apparatus 200 is discharged to the developer cartridge 6 by the utilization of a change in a gravity acting direction due to the rotation of the rotational type developing member 101′. That is, the supply and collection of the developer are effected by the utilization of rotational motion peculiar to the rotational type developing member 101′ and therefore, structure is simple and any reduction in the charging ability of the carrier is prevented without causing the bulkiness of the multi-color image forming apparatus and a rise in cost.
On the other hand, in Japanese Patent Application Laid-Open No. H10-142888, as shown in FIG. 11 of the accompanying drawings, four developing apparatuses 200 are likewise provided in a rotational type developing member 101′, and design is made such that at a developing position P1 whereat a developing apparatus 200 is opposed to a photosensitive drum 113, a developer discharged from the developing apparatus 200 is temporarily stored in a storing portion 70 protrudedly provided on an end portion of the developing apparatus 200, and is carried to the central cylinder shaft D0 of the rotational type developing member 101′ by the utilization of a change in a gravity acting direction due to the rotation of the rotational type developing member 101′, and is finally collected in a developer collecting container (not shown) provided on an end of the cylinder shaft D0 by a developer carrying member D1 in the cylinder shaft D0. That is, as in the multi-color image forming apparatus proposed in Japanese Patent Application Laid-Open No. H9-218575, the discharge of the developer is effected by the utilization of movement peculiar to the rotational type developing member 101′ and therefore, any reduction in the charging ability of the carrier is prevented without causing the bulkiness of the multi-color image forming apparatus, and design is made such that even when single-color image forming is continued, at the developing position P1, any excess developer in the developing apparatus 200 is discharged to a storing portion 70 outside the developing apparatus 200 without the developing operation being stopped and therefore, the amount of developer in the developing apparatus 200 is maintained within an allowable value without image productivity being reduced.
In the developing apparatuses having the excess developer discharging construction as described above, there has been adopted a construction in which when the level of the developer has become higher than the prescribed level of the developer in a developing container, the developer is scooped out by the utilization of the rotational motion of the rotational type developing member (see, for example, Japanese Patent Application Laid-Open No. H9-218575), or a construction in which the excess developer is once collected in a storing portion, and then is collected in a location by the utilization of the rotational motion of the rotational type developing member (see, for example, Japanese Patent Application Laid-Open No. H10-142888).
Besides these, in the latent multi-color image forming apparatuses, a higher speed and a higher quality of image are required and toward a higher speed, the rotational speed of an image forming process system is heightened, that is, the rotational speed of an agitating member (developing screw) in the developing apparatus is heightened, and toward a higher quality of image, the rotational speed of the developing screw in the developing apparatus is heightened in an attempt to obtain uniform agitation.
With the market of full-color copying machines/printers having been enlarged in recent years and various functions being required, many multi-color image forming apparatuses having the compactness and lower cost of the apparatus and yet seeking after high image productivity have been produced and in the future as well, they seem to become one of the mainstreams of the market.
Also, when a higher speed is aimed at, the rotatable time of the rotational type developing member tends to be extremely shortened, and a shock applied to the developing apparatus tends to become great. Besides these, as the rotation stop positions of the rotational type developing member, usually in addition to a developing position during continuous image forming, there is a home position in which a developing sleeve is retracted to a location spaced apart from a photosensitive drum which is an image bearing member, as for a rotational type developing member of a type having a developer cartridge in the interior of the rotational type developing member, there is further a stop position exclusively for the interchange of the developer cartridge.
Under such a situation, it is self-evident that the art of a developing apparatus for effecting the supply of a developer containing a toner and a carrier and the collection of any excess two-component developer which is simple in structure and which prevents any reduction in the charging ability of the carrier and suppresses any increase in service cost and running cost without causing the bulkiness of the multi-color image forming apparatus and a rise in the cost thereof will also be positioned as important art in the future.
Now, as shown in FIGS. 10 and 11, in these developing apparatuses 200, there have been seen many constructions which have a first agitating chamber R1 on a developing sleeve side which is a developer carrying member (developing sleeve) 8 for carrying the developer to a developing area and a second agitating chamber R2 on a side having a supplying port and in which the developer is circulated between the first agitating chamber R1 and the second agitating chamber R2 by an agitating member 7.
If in such constructions, an excess developer discharge port 1 is provided on the first agitating chamber side, discharge can be hardly effected under the influence of the magnetic force of a magnet roll disposed in the developing sleeve 8, or the carrier which originally should be discharged will be sucked and only the toner which should not be discharged will be discharged. Also, even if the excess developer discharge port 1 could be disposed on the first agitating chamber side with a sufficient distance kept from the magnet roll, only the level of the developer near the discharge port 1 in the direction of the rotary shaft of the developing sleeve 8 will lower and the supply of the developer to the developing sleeve 8 will become little and only that portion will become low in density. Therefore, in the developing apparatuses described in the aforedescribed examples of the conventional art, it is often the case that the excess developer discharging construction is provided in the second agitating chamber R2.
In such an excess developer discharging mechanism, the excess developer discharging position of the developing apparatus 200 is set to the developing position P1. Accordingly, during excess developer discharge, the agitating member 7 in the developing apparatus 200 agitates and carries the two-component developer in the developing apparatus 200 while being rotated, and circulates the two-component developer in the developing apparatus 200.
Also, while a description has been made of the discharge of the two-component developer utilizing the force in the gravity acting direction resulting from the rotational motion of the rotational type developing member 101′, the conventional art is not restricted to the rotational type developing member 101′.
As shown in FIGS. 15A and 15B, it has heretofore also been practiced to control the height of the developer level in an agitating chamber to thereby discharge the two-component developer. The developer stagnates by narrowing the screw pitch interval downstream of the discharge port. Thereby the height of the developer level in the discharge port swells and the developer exceeding a prescribed height is discharged.
However, in the conventional developing apparatuses 200 described in Japanese Patent Application Laid-Open No. H6-308829 and Japanese Patent Application Laid-Open No. H9-218575, if the number of revolutions of the agitating member 7 in the developing apparatus 200 is increased aiming at the recent higher speed and higher quality of image, it will gradually become difficult for the developer level in the developing apparatus 200 to be stable, and stable discharge will gradually become difficult.
Particularly, in a multi-color image forming apparatus having the rotational type developing member 101′, the shortening of the rotated position changeover time of the rotational type developing member 101′ is advanced to cope with the high productivity in recent years. In this case, the impact force during the start and stop of the rotation of the rotational type developing member 101′ tends to become great, but in the other rotation modes than a continuous image forming operation, there is often seen a case where an acceleration-deceleration curve is set gently in an attempt to make the impact force small. In a case where the rotational type developing member 101′ has a plurality of rotation modes as described above, the instability of the discharging mechanism resulting from an increase in the rotation stop position tends to be further promoted.
This is because the developer level state in the developing apparatus 200, as compared with a case where the agitating member 7 has been rotated from the horizontal stationary state of the developing apparatus 200, remarkably differs in situation in a case where the agitating member 7 has been rotated from a state accompanied by the revolving operation of the rotational type developing member 101′, and much time is taken until the developer level state becomes stable at an ordinary developer level from the start of the rotation of the agitating member 7.
Also, in the conventional excess developer discharging construction, it sometimes happens that during the time until the level of the developer becomes stable, the developer being at a position higher than a predetermined developer level is discharged in spite of being not the excess developer.
Now, in multi-color image forming apparatuses having a rotational type developing member, there has often been seen a construction in which a developing sleeve provided in a developing apparatus is stopped and is made to wait at a phase position (so-called home position) in which it is not opposed to a photosensitive drum so that the photosensitive drum may not be adversely affected by the strong magnetic force of the developing sleeve when the image forming operation is not being performed.
Also, when the rotational type developing member assumes a construction including a developer cartridge 6 constituted by a toner bottle containing therein a developer to be supplied, there has been seen a case where the phase position at which the developing member is stopped and waits in order to interchange the developer cartridge 6 is provided at a phase position discrete from a developing position and a home position stop and waiting position.
When such a construction is adopted, a plurality of stop and waiting positions further become necessary besides the developing positions for respective colors. For example, the stop positions of a rotational type developing member holding developing apparatuses for four colors are not restricted to four positions, i.e., 0 degree as the developing position, and 90 degrees, 180 degrees and 270 degrees therefrom, but unavoidably the construction must have a plurality of stop positions in addition to these.
Not to speak of a case where a three-color rotary construction (in this case, equal rotations by 120 degrees+α) is adopted when in view of the recent use situation of offices, an attempt is made to develop a multi-color image forming apparatus laying emphasis on black-and-white continuous images, or a case where there are given toner cartridge interchanging positions which are unequal from the stop position during ordinary continuous image forming, it is already becoming an indispensable technique for the rotational type developing member to be stopped at a plurality of rotation stop positions.
However, both of the multi-color image forming apparatus described in Japanese Patent Application Laid-Open No. H9-218575 and the multi-color image forming apparatus described in Japanese Patent Application Laid-Open No. H10-142888 are of a construction in which the developers are made to fall by the utilization of a change in the gravity direction by the rotational movement of the rotational type developing member and therefore, it sometimes happens that the more are increased the rotation stop positions, the more unstable becomes the height position of the developer level, and unexpected discharge takes place or the developer cannot be discharged when it should be discharged, and it becomes difficult to maintain a high quality of image. It is because of a construction in which during a continuous image forming operation, the aforedescribed developing stop position visits periodically stably, whereas the home position waiting position visits only after the termination of the job, and the developer cartridge interchange stop and waiting position visits only when the amount of the toner in the cartridge has become small.
If an attempt is made to obtain a discharging characteristic which includes all these conditions and yet is stable, very much time is required for the setting of the conditions, and this has greatly affected the shortening of the developing period.
In the multi-color image forming apparatuses described in the aforementioned Japanese Patent Application Laid-Open No. H9-218575 and Japanese Patent Application Laid-Open No. H10-142888, the deteriorated developer is discharged into the developer cartridge by the utilization of the rotational motion of the rotational type developing member and therefore, structure is simple, and the bulkiness and high cost of the multi-color image forming apparatus are not caused, and the deteriorated developer is gradually replaced with a fresh developer to thereby stabilize the characteristic as the entire developer.
However, although the interchange of the developers becomes unnecessary and the maintenance property is improved, the rotating operation of the rotational type developing member must be performed to stably discharge the excess developer in the developing apparatus to the outside of the developing apparatus, and under the influence of the instability of the level of the developer in the developing apparatus resulting from the increase in the number of the rotation stop positions, a great reduction in image productivity could not be avoided.
Also, these multi-color image forming apparatuses are of a construction in which a storing portion must be discretely provided in the developing apparatus, and such construction, in spite of being an unnecessary member for ordinary image forming, need be contrived to ensure good discharge as the number of the rotation stop positions is increased as described previously, and it is unavoidable for the construction to gradually become complicated and large-scale, and the complication of the multi-color image forming apparatus and a rise in the cost thereof could not be avoided.
However, both of the multi-color image forming apparatus described in Japanese Patent Application Laid-Open No. H9-218575 and the multi-color image forming apparatus described in Japanese Patent Application Laid-Open No. H10-142888 are of a construction in which the developers are made to fall by the utilization of a change in the gravity direction by the rotational movement of the rotational type developing member and therefore, it sometimes happens that the more are increased the rotation stop positions, the more unstable becomes the height position of the developer level, and unexpected discharge takes place or the developer cannot be discharged when it should be discharged, and it becomes difficult to maintain a high quality of image. It is because of a construction in which during a continuous image forming operation, the aforedescribed developing stop position visits periodically stably, whereas the home position waiting position visits only after the termination of the job, and the developer cartridge interchange stop and waiting position visits only when the amount of the toner in the cartridge has become small.
Besides these, in the aforedecribed excess developer discharging construction, such parameters as the height and area of the discharge port, the number of revolutions and pitch of the agitating member are conceivable as parameters which can set conditions to obtain a desired developer discharge amount, but the number of revolutions and pitch of the agitating member greatly affect the two-component developer supplied to the developing sleeve (the higher speed progressed for the higher quality of image is a good example of it) amd therefore, it has been impossible in reality to change these parameters for the adjustment of the excess developer discharge amount. Thereupon, after all, the parameters which can set conditions are restricted to such limited conditions as the height and area of the discharge port, and it is the present situation that actually sufficient condition setting could not be done due to a combination of other design factors.
That is, in the conventional art, the work of interchanging the developer becomes unnecessary and the maintenance property is improved, but is has been difficult to obtain a stable high image quality maintaining characteristic, and it has been impossible to realize both of the simplification and lower cost of the multicolor image forming apparatus and high image productivity at a time.